Blasting charge composition



April 16, ,1957 w. MAXWELL Erm. 2,789,043

BLASTING CHARGE COMPOSITION Filed Feb. 4, 1954 mL-Mu mxwel. L Owen ALLI/,v .101m sun ron ATTORNEYS United States Patent() 2,789,043 BLASTING CHARGE coMrosrrloN William Maxwell, Stevenston, and Owen Allen John Gurton, Fairlie, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application February 4,1954, Serial No. 408,102 I Claims priority, application Great Britain April 30, 1953 1 Claim. (Cl. 52-14) lThe presentl invention relates to compositions suitable for use as blasting charges in re-utilisable blasting as semblies and which are particularly suitable for use as blasting charges in dusty or lery mines and which are capable of undergoing self-sustained ameless gas-producing thermal decomposition when locally heated under pressure.

Blasting devices have been Widely used which comprise a pressure resisting container of tubular construction which is closed or fitted with a gas-tight closure at one end and fitted at the other end with a venting cap separated from the container by an expendable `bursting disc adapted to yield at a predetermined pressure and which is fitted with electrical contacts to enable a local heating element to be electrically actuated. In a blasting device of this kind the blasting effect is produced by the discharge of the gases into the borehole through ports in the venting cap when the pressure within the container has built up suiiiciently to cause the bursting disc to yield and a passage has been opened up between the container and the venting cap. The time taken for the discharge of the gases from the container into the venting cap and through the ports into the borehole after the yielding of the bursting disc is sulcient to result in a comparatively gentle heaving blasting eiect, such as is desirable for such purposes as the production of lump coal.

In blasting devices of the aforementioned kind the charge commonly used consists essentially of an equimolecular mixture of sodium nitrite and ammonium chloride stabilised with an alkali such as magnesium oxide or sodium carbonate in amounts up to about 3% by weight. These charges when locally heated decompose in a nondetonating manner without llame in self-sustained fashion with the formation of sodium chloride, nitrogen and steam and under the rising pressure conditions experienced in the aforesaid blasting device this decomposition once initiated by the local heating element is greatly accelerated and almost immediately the gases are discharged without llame. This charge is initiated by a heating element which is normally a small electric blackpowder fuse. This practice has been possible because although a blackpowder fuse produces flame,` the time taken for the decomposition of the stabilised mixture of sodium nitrite and ammonium chloride to build up a pressure suficient to cause the bursting disc to yield is long enough for the fragments of the electric fuse to have burned out before the bursting disc yields.

Compositions based on mixtures of ammonium chloride and sodium nitrite are capable, when their decomposition is initiated by local heating to a moderately raised temperature, of supporting their gas generating decomposition at a visible rate throughout the whole mass of the composition even at atmospheric pressure. This is a distinct disadvantage for some purposes since in the event of any portion of a mass of the composition being heated accidentally the whole mass may react and produce dense clouds of unpleasant fumes. Thus under- 2,789,043 ,Ptented Apr. 16, 1957i ICC ground loading'of these charges in coal mines is'not at present practicable. It is, therefore, desirable to obtain compositions capable of undergoing self-sustained decomposition only when initiated under pressure. e

According to the present invention a blasting compofl sition suitable for useas a main charge in blasting devices of the aforesaidvv kind comprises ammonium nitrate, in amount from 550 to 75.0% by weightand calcium' formate in amount from 45.0 to 25.0% by weight with,` if desired, calcium stearate in amount up to 0.5% by; weight. Y v .l 1

The invention alsoresides in a blastingfdevice which comprises a tubular container closed or fitted with a gas-' tight closure at one end and havinga venting cap .at the, other end, said venting cap being separated from communication with said container by an expendable bursting disc adapted to yield at a predetermined pressure, an electrically actuable local heating device, means for, permitting pressure to be formed'twithin the container and a main blasting charge comprising 55.0 to 75.0% by weight ammonium nitrate .and 45.0 to .25.0%Y byweight calcium formate with, if,desired,'up to '0.5%'. by weight calcium stearate.

The means for permitting pressure to be formed within the container may be the said local heating device. Thus a gas-producing electrically actuable local heating device which will produce at least sufiicient hot gas to raise the pressure within the pressure resisting container to several atmospheres may be, for example, a safety heating device as claimed in co-pending application Serial No. 397,328, December 10, 1953, now abandoned, wherein an electric initiating element and a heating composition are enclosed in a container and is characterised in that the heating composition comprises 66 to 45% by weight guanidine nitrate, 27 to 45% by weight potassium persulphate and 6 to 10% by weight cuprous chloride with, if desired, up to 1% by weight petroleum jelly and in that the container is adapted to release the gas formed within it on initiation of said heating composition. On the other hand the means for permitting pressure to be formed within the container may comprise for example a holder adapted to deliver gas under pressure and a non-return valve connected thereto and to an inlet into the container so as to permit the desired quantity of gas to be introduced into said container.

The heating device used with the composition of the invention is preferably one which will generate suiiicient hot gas to raise the pressure inside the pressure resisting container to several atmospheres. Other kinds of heating devices can, however, be used.

The ameless gas generating charge compositions of the present invention have the great advantage that their decomposition can only be initiated if under pressure and will not initiate at atmospheric pressure. Thus they differ from the hitherto used compositions based on mixtures of ammonium chloride and sodium nitrite in that they are incapable of sustaining their own thermal decomposition through a mass as a result of mere local heating of a portion thereof at atmospheric pressure, so that even if a hot object should accidentally come into contact with a portion of a mass of the composition in a mine at atmospheric pressure decomposiiton will not be initiated. The fume produced in the blast is less in amount and less persistent than that obtained from compositions based ou ammonium chloride and sodium nitrite and the gases are satisfactorily free from poisons or irritating constituents. The total amount of solid products formed is also much smaller than that formed from ammonium chloride/sodium nitrite compositions. Furthermore, any gaseous or solid materials projected are at too low a temperature teL ignite-.tiery/or. Idusty aunospheres or to i etnistituteI any` indirect ignitionv risk.

For use in blasting devices of the aforesaid kind the compositions of the present invention maybe enclosed ihr 2'.fecmtai'rusx'which is preferably# made ofYA any con.- venie'nt non-deagratingtfnon-smoulderale-fmaterial `such -astsheetemetakcertain synthetic plastics suchas the-poly ethylene polymers, certain rsynthetic resins such as"V polyeliloracrylatesaorreproofed cardboardv but maybe of combustiblematerialsprovidedVthat-the combustion-there# oc'aigmotA be'initiatedbyrthe heat of'lthe. decomposition. This'containermaybe so shaped that italso-contains 'the localheating..element andf thusv enablesthe complete- 'charge "tot be pre-packaged and? makes loadingy easier-andi faster than has formerly been possible. v

\ The invention i'sf'illustrated by" the. following Vexample inwhiclt-all percentages are by weight and with reference to' Ihcdagiammat'c drawing attached hereto.

. Afpressureresistingtsteel containerl s-o680 ml. ca ofltneh. internal; diameter-and is provided with' at-.hurstngdisc ZiofthieknessF/inch adapted toabnrstfat apxessure; of E1 12 tonsl/sq.-v in., avuseheadlf'andia discharge headxt.. walveznlent:v compositionV 5 tzonsists.'v of I a of 21053111.- of acomposition consisting-of 65.0%

ammonium nitrate (containing 0.05% acid magenta), 343% calciur11-formateand` 0.1%- calciumstearate packed in a glazed paper tube 6 of0.9 inch in diameter and 23 inches long into the centre of which is embedded a local heating device 7 consisting of 22.5 gm. of a mixture of 60.0% guanidine nitratel,`31.5%nu potassium pei-sulphate, 8.0% by weight cuprous chloride and 0.5% petroleum jelly wrapped infar ireproofed,manillarY envelope Vand provided with electrical actuating means. When the pres-- sure. resisting: container 1 thus'loaded is utilised lin Va borehole in known manner theV bl'ast takes place withinu 4 seconds with little fume and: the fume `evolved'is relatively free f rompoisonous and inizitatingcon'stituents.

Whatwe claim is; Y Y

A pulverulent, non-detonating gas generating composition suitable for usev iure-utilizable blasting devices consisting essentially of ammonium nitrate in amount from about 55 to 75% by weight, calcium formate in amount from: about 25 to 45% by Weight, and calcium stearate in amountupA to about 0.5% by weight;

Germany Sept. 3', 1923' Great Britain'- Mar. 4, 11938 

